This disclosure relates to toner and a method of forming images utilizing electrophotographic photoreceptors. More in particular, the disclosure relates to toner having specific external additives in order to improve the performance characteristics of electrophotographic photoreceptors. Specifically, the rotational torque is reduced while the amount of deletion in the developed image is decreased.
Electrophotographic method has been generally used when an image is formed in copier or a laser beam printer. In conventional electrophotographic image forming methods, an image is formed by developing an electrostatic latent image formed on a photoreceptor with a toner developer. The electrostatic latent image is then transferred to an image receiving member such as recording paper. Next, the electrostatic image is fixed to the image receiving member using heat and pressure.
Methods for developing the electrostatic latent image include a one-component developing method, which uses only a toner. Also known is a two-component developing method, which uses a toner and a carrier. In the case of the two-component developing method, the toner and the carrier are stirred to triboelectrically charge the toner. Therefore, the amount of triboelectric charge of the toner can be controlled to a considerable extent by selecting carrier characteristics and stirring conditions.
The toners conventionally used in the electrophotographic process may be produced by various methods. For example, toners may be produced by adding various resins (e.g., polyester resin, styrene-acryl resin, and epoxy resin), colorants, charge control agents, releasing agents and the like, and then melting, kneading, and uniformly dispersing the mixtures. This is followed by crushing the mixture into a predetermined grain size and removing excessively coarse powders and micropowders using a classifier. Toners may also conventionally be produced by chemical methods, such as by the suspension polymerization method, and an emulsion polymerization coagulation method.
U.S. Pat. No. 6,319,647 discloses a toner including toner particles containing at least one binder, at least one colorant, and preferably one or more external additives. The toner is advantageously formed into a developer and used in a magnetic brush development system to achieve consistent, high quality copy images. The toner particles, following triboelectric contact with carrier particles, exhibit a charge per particle diameter (Q/D) of from 0.6 to 0.9 fC/μm and a triboelectric charge of from 20 to 25 μC/g. The toner particles preferably have an average particle diameter of from 7.8 to 8.3 microns. The toner is combined with carrier particles to achieve a developer, the carrier particles preferably having an average diameter of from 45 to 55 microns and including a core of ferrite substantially free of copper and zinc coated with a coating comprising a polyvinylidenefluoride polymer or copolymer and a polymethyl methacrylate polymer or copolymer. In this developer, the fluoropolymer is on the carrier coating.
U.S. Pat. No. 6,416,916 discloses a toner made of toner particles containing at least one binder, at least one colorant, and an external additive package comprised of zinc stearate and at least one of silicon dioxide or titanium dioxide, wherein the amount of zinc stearate is limited to about 0.10 percent by weight or less of the toner. It is reported that when the amount of zinc stearate is limited, a developer formed from the toner exhibits excellent triboelectric charging, stability and developer flow.
U.S. Pat. Nos. 6,797,448 and 6,692,880 disclose a development system for toner that includes a toner having at least one toner resin, at least one release agent, at least one surface treatment, and optionally at least one charge control agent or colorant or both. The surface treatment, also known as spacer particles, includes acrylic polymer, silicone-based polymer, styrenic polymer, fluoropolymer, or mixtures thereof.
The photoreceptor used in electrophotography may comprise a single layer configuration or a multi-layered structure. For example, an electrophotographic photoreceptors having dual layer structure comprises two layers consisting of a charge generation layer and a charge transport layer. Since the photoreceptor is used repeatedly, a cleaning device is typically disposed to remove residual toner left on the photoreceptor after the transfer. In the aforementioned image forming method, the characteristics of the photoreceptor are adversely affected due to various causes, such as surface deterioration caused by charging device, wear due to abrasion, reduced sensitivity and reduced charging ability caused by the electrical impact of discharging at the photoreceptor surface, and mechanical breakdown resulting from friction during subsequent toner development, transfer to paper, and cleaning. In order to improve the durability of the photoreceptor, a protective overcoat with a highly crosslinked polymer composition is applied. The overcoat layer had overwhelmingly superior chemical stability and mechanical strength with respect to conventional surface layers, whereby deterioration of the surface layer caused by wear can be significantly reduced and longevity can be improved.
U.S. Pat. No. 5,681,679 discloses a flexible electrophotographic imaging member including a supporting substrate and a resilient combination of at least one photoconductive layer and an overcoat layer. The photoconductive layer includes a hole transporting arylamine siloxane polymer and the overcoat includes a crosslinked polyamide doped with a dihydroxy amine. This imaging member may be utilized in an imaging process including forming an electrostatic latent image on the imaging member, depositing toner particles on the imaging member in conformance with the latent image to form a toner image, and transferring the toner image to a receiving member.
U.S. Pat. No. 5,368,967 discloses an electrophotographic imaging member comprising a substrate, a charge generating layer, a charge transport layer, and an overcoat layer comprising a small molecule hole transporting arylamine having at least two hydroxy functional groups, a hydroxy or multihydroxy triphenyl methane and a polyamide film forming binder capable of forming hydrogen bonds with the hydroxy functional groups the hydroxy arylamine and hydroxy or multihydroxy triphenyl methane. This overcoat layer may be fabricated using an alcohol solvent. This electrophotographic imaging member may be utilized in an electrophotographic imaging process. Specific materials including Elvamide polyamide and N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine and bis-[2-methyl-4-(N-2-hydroxyethyl-N-ethyl-aminophenyl)]-phenylmethane are disclosed in this patent.
Silicon overcoat layers (“SOC”), as disclosed in co-pending U.S. patent application Ser. No. 11/034,062, and incorporated herein by reference in its entirety, have demonstrated good potential for the life extension of photoreceptors. Owing to its crosslinked siloxane structure, SOC offers excellent abrasive, scratching and marring resistance. The SOC is typically prepared by curing a sol-gel type coating solution comprising a silane-containing hole transport molecule and an organic silane matrix binder.
While the photoreceptor having a SOC protective layer provides initial satisfactory image quality, its image quality deteriorates after repeated printing. It has been theorized that this deterioration occurs because the surface of a photoreceptor with low abrasion resistance possesses high coefficient of friction when the surface of the photoreceptor is cleaned with a rubber blade in a cleaning step, such as a urethane blade. This leads to blade damage and image defects.
Furthermore, when the siloxane surface layer is used for a long period of time, especially in a humid environment, image defects, such as image deletion, are caused.
It is theorized that after exposure to charging for a long period of time in a humid environment, the SOC surface of the photoreceptor becomes hydrophilic as the siloxane surface is denatured by the action of the ozone and NOx generated during the charging process. The deteriorated surface tends to adsorb moisture in the atmosphere, causing the electrical resistance of the surface to be microscopically reduced and difficulty in maintaining the electrostatic latent image.
Thus, it is still desired to improve the durability of the photoreceptor by providing an improved toner additive, an improved image forming method and an improved image forming apparatus.